1. Field
The present disclosure relates generally to electric motor systems and, in particular, to controlling electric motor systems. Still more particularly, the present disclosure relates to a method and apparatus for controlling the emitted signature of an electric motor system.
2. Background
An electric motor is a device that converts electrical power into mechanical power. Electric motors are used for various applications. These applications include fans, pumps, tools, disk drives, drills, and other types of devices that may be found in these and other types of platforms.
A brushless electric motor is a commonly used type of electric motor. With brushless electric motors, a controller is configured to change the current in windings in the electric motor. In particular, the current is switched at a frequency that changes the amplitude of the current applied to the windings in phases in a manner that causes the motor to turn. The switching of the current is performed using switches in the form of transistors. These transistors may be located on an inverter board in the electric motor system.
Often, multiple brushless electric motors are used in an electric motor system. The operation of brushless electric motors in the electric motor system may result in a signature generated by the electric motor system. Each of the brushless electric motors may generate an individual signature that forms the overall signature of the electric motor system. This signature may include electromagnetic, acoustic, and thermal signatures.
For example, the switching of the current for brushless electric motors by transistors in an inverter board in the electric motor system may generate electromagnetic signals, acoustic signals, or both. In some cases, the switching frequency may be in the range of human hearing. The frequencies of the acoustic signals generated by the operation of brushless electric motors may coincide in a manner that results in an acoustic signature that may disturb persons near the brushless electric motors. In other words, the noise generated by the brushless electric motors may be greater than desired.
As another example, switching of the current for brushless electric motors may generate electromagnetic signals. These electromagnetic signals generated by the different brushless electric motors may coincide in a manner that results in a large spike in the magnitude of the electromagnetic signals. As a result, the electromagnetic signature of an electric motor system may be greater than desired.
Currently, one manner in which the acoustic signature of an electric motor system may be reduced is through the use of soundproof insulation in a housing that encloses the brushless electric motors, inverter board, or both. With respect to the electromagnetic signature, the components may be enclosed in a Faraday cage.
These types of solutions, however, may increase the weight, bulk, cost, or a combination of these factors for the electric motor system. When these types of factors are important, such as in an aircraft, the currently available solutions may be less than desirable.
Therefore, it would be desirable to have a method and apparatus that take into account at least one of the issues discussed above as well as possibly other issues.